High voltage resistor



April 29, 1969 MAKOTO YAMAMOTO ET AL HIGH VOLTAGE RESISTOR Filed April30, 1968 WATAN ABE FIG-3 Em: B

United States Patent Oflice Patented Apr. 29, 1 969 3,441,894 HIGHVOLTAGE RESISTOR Makoto Yamamoto, Minoru Fujisawa, and Eiji Watanabe,Tokyo, Japan, assignors to Nihon Denshi Kabushiki Kaisha, Tokyo, Japan,a corporation of Japan Continuation-impart of application Ser. No.511,984, Dec. 3, 1965. This application Apr. 30, 1968, Ser. No. 725,379Claims priority, application Japan, Dec. 10, 1964, 39/ 69,554 Int. Cl.H01c 1/02 US. Cl. 338-431 10 Claims ABSTRACT OF THE DISCLOSURE A highvoltage resistor including a resistor immersed in oil and surrounded bya cylinder of electrically conductive material. Between the resistor andcylinder is an insulating corrugated bafile for restraining movement ofthe oil when a voltage is applied to the cylinder, to reduce noise andchange in voltage value between the input and output of the resistor. Asecond cylinder of conductive material can be positioned around thefirst cylinder and connected in the same manner. In an embodiment of theinvention, the first cylinder can be made of a suitable resistancematerial connected directly to the input and grounded whereby thepotential drop across the resistor and the cylinder can be equalized tosubstantially eliminate oil turbulence and corona discharge.

This application is a continuation-in-part of our United States patentapplication Ser. No. 511,984 filed Dec. 3, 1965, now abandoned.

This application relates to a high voltage resistor which isparticularly useful in a negative feedback circuit used to maintain thestability of a high voltage source. Such a voltage source may be used asthe electron accelerating voltage in an electron gun used in an electronmicroscope or electron diffraction apparatus. In such apparatus thevoltage should not vary more than one part in a million.

Resistors used in negative feedback circuits have high resistance valuesand extremely high voltages are applied to them. Consequently, leakagecurrents develop between the input and output leads of the resistoracross the outer surfaces of the resistors. To reduce these leakagecurrents the resistors are immersed in tanks of oil.

However, the extremely high voltage between the input and output leadscause movement of the oil and this movement produces changes inelectrostatic and electromagnetic fields existing in the oil around theresistor, and these changes in the electrostatic and electromagneticfields create changes in the value of the resistor which are known asnoise, and this noise changes the value of the voltage between the inputand output value of the resistor.

We have invented a high voltage resistor which is immersed in oil and inwhich movement of the oil surrounding the resistor is greatly reduced ascompared to similar conventional resistors.

In the accompanying drawings, we have illustrated two presentlypreferred embodiments of the invention in which:

FIGURE 1 is a vertical section through one embodiment of our invention;

FIGURE 2 is a vertical section through a second embodiment of ourinvention; and

FIGURE 3 is a partial vertical section of another embodiment of ourinvention.

Referring to FIGURE 1 of the drawing, a resistor 1 having a highresistance value is placed in a tank 2 which is grounded and [filledwith insulating oil 3 and which is made of iron, copper, aluminum, etc.A cylinder 4 of electrically conducting material such as iron, copper,aluminum, etc. surrounds the resistor. A corrugated baffle 5 ofinsulating material extends between the resistor 1 and the cylinder 4.Discs 13a and 13b of insulating material support and position theresistor 1, the cylinder 4 and the battle 5 with respect to each otheras shown in FIGURE 1.

A high voltage input lead 9 extending through a bushing 10 of insulatingmaterial which extends through the top of the tank 2 is connected to oneend of the resistor 1 through wire 11.

An insulator 12 surrounds the wire 11 and supports the insulating disc13a.

An output lead .14 is connected to the other end of the resistor 1 andextends through the oil 3 in the tank 2 out through the top of the tank.The lead 14 has a grounded shield 8 to reduce noise.

Two capacitors 6 and 7 have a common connection with the cylinder 4. Theother lead of the capacitor 6 is connected to the input wire 11, and theother lead of capacitor 7 is grounded by connection to the tank 2.

By reason of the connections just described the voltage between theresistor 1 and the cylinder 4 is approximately one half that existingbetween the resistor and the tank 2. The movement of oil between theresistor and the cylinder is proportionately reduced and changes inelectrostatic and electromagentic fields induced by movement of oil arecorrespondingly reduced. The bafile 5 further reduces the movement ofoil.

FIGURE 2 shows a second embodiment of our invention which is the same asFIGURE 1 except that a second cylinder 15 of conductive material ispositioned in the tank 2 around the first cylinder 4. Voltage is appliedto the cylinder 15 through capacitors 16 and 17 and lead 18 in the samemanner that a voltage is applied to the cylinder 4.

Since cylinders 4 and 1'5 are at the same potential, there 's nomovement of the oil between them. Therefore, no changes in electrostaticand magnetic fields around the cylinder 4 are induced and noise isreduced to zero.

FIGURE 3 shows a partial vertical section of another embodiment of ourinvention in which a cylindrical resistance material 19, which is,readily available on the market is used instead of the electricallyconducting material 4 in FIGURES 1 and 2- In this case, the input lead18 is connected directly to the upper end of the cylinder and the lowerend of the cylinder is grounded by connection with the tank (not shown).No capacitor is used. If cylinder 19 is made of a suitable resistancematerial, the potential drop across the resistor and the cylinder can beequalized, thus enabling the potential gradient of the space between theresistor and the cylinder to be almost zero in the radial direction. Asa result, corona discharge and oil turbulence are almost eliminated.

In addition to achieving voltage stability, our resistor has the furtheradvantage that for a given capacity resistor the size of the oil tankcan be reduced. It is not necessary to make the tank large in order toobtain a high value of resistance for the oil.

While we have described certain presently preferred embodiments of ourinvention, it is to be understood that they may be otherwise embodiedwithin the scope of the appended claims.

We claim:

1. A high voltage resistor comprising,

(A) a resistor;

(B) input and output leads connected to said resistor;

(C) a tank containing oil in which said resistor is positioned andthrough which said leads extend;

(D) an electrically conductive cylinder positioned in said oil andsurrounding said resistor;

3 (E) a bafile positioned between the resistor and the cylinder torestrain movement of oil between the resistor and cylinder; and (F)means for applying a voltage to said cylinder which is less than thevoltage between said input and output leads.

2. A high voltage resistor as described in claim 1 in which the meansfor applying voltage to said resistor comprises two capacitors, eachcapacitor having a lead connected to said cylinder, the other lead ofone of said capacitors being connected to the input lead and the otherlead of the other capacitor being connected to ground.

3. A high voltage resistor as described in claim 1 and havingelectrically insulating means for closing the ends of said cylinder tofully enclose said resistor.

4. A high voltage resistor as described in claim 1 and having a secondcylinder surrounding the first cylinder and means for applying a voltageto said second cylinder which is less than the voltage between saidinput and output leads.

5. A high voltage resistor as described in claim 1 and having a secondcylinder surrounding the first cylinder and means for applying a voltageto said second cylinder which is equal to the voltage applied to thefirst cylinder.

6. A high voltage resistor as described in claim 4 and havingelectrically insulating means to close the ends of both cylinders andfully enclose said resistor.

7. A high voltage resistor as described in claim 4 in which the meansfor applying a voltage to the second cylinder comprises two capacitors,having a common connection with said second cylinder, one of saidcapacitors being connected to the input lead and the other of saidcapacitors being connected to ground.

8. A high voltage resistor comprising,

(A) a resistor;

(B) input and output leads connected to said resistor;

(C) a tank containing oil in which said resistor is positioned andthrough which said leads extend;

(D) a cylinder of resistance material positioned in said tank andsurrounding said resistor;

(E) a baflle positioned between the resistor and the cylinder torestrain movement of oil between the resistor and the cylinder; and

(F) leads for connecting said cylinder to said input lead and to ground.

9. A high voltage resistor as described in claim 8 and havingelectrically insulating means for closing the ends of said cylinder tofully enclose said resistor.

10. A high voltage resistor as set forth in claim 8 and having a secondcylinder surrounding the first cylinder, means for applying a voltage tosaid second cylinder and electrically insulating means to close the endsof both cylinders and fully enclose said resistor.

References Cited UNITED STATES PATENTS 10/1906 Waters 33823l 2/1941Brooks.

US. Cl. X.R. 338334; 317---256

